<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="../js/vue.js"></script>
</head>

<body>
  <div id="app">
    <h1>空气净化器</h1>
    <h2>{{pm25}}</h2>
    <img v-if="pm25<100" src="../img/1.png">
    <img v-else-if="pm25<200" src="../img/2.png">
    <img v-else-if="pm25<300" src="../img/3.png">
    <img v-else src="../img/4.png">
  </div>
  <script>
    var vm = new Vue({
      el: "#app",
      data: {
        pm25: 180
      },
      created() {
        setInterval(() => {
          let pm25 = Math.random() * 400;
          this.pm25 = Math.round(pm25);
        }, 2000);
      },
    });    
  </script>
</body>

</html>